Method of making elastic articles having improved heat-resistance

ABSTRACT

The present invention relates to a method for making a heat-resistant elastic article and a heat-resistant elastic article. The invention especially relates to a method of making elastic fibers and polymeric elastic fibers wherein the elastic fibers are capable of withstanding dyeing and heat-setting processes that typically are conducted at elevated temperatures (such as 110-230° C. and especially at greater than or equal to 130° C. for minutes). The inventive method comprises radiation crosslinking an article (or plurality of articles) under an inert or oxygen limited atmosphere (for example, in N 2 , argon, helium, carbon dioxide, xenon and/or a vacuum) wherein the article (or articles) comprises at least one amine stabilizer and preferably another optional stabilizer additive. More preferably, the radiation crosslinking is performed at a low temperature (−50 to 40° C.). The elastic article (or articles) comprises a homogeneously branched ethylene interpolymer (preferably a substantially linear ethylene interpolymer), a substantially hydrogenated block polymer, or a combination of the two. The heat-resistant elastic articles (especially fibers) are useful in various durable or repeated-use fabric applications such as, but not limited to, clothing, under-garments, and sports apparel. The heat-resistant elastic fibers can be conveniently formed into fabrics using well-known techniques such as, for example, by using co-knitting techniques with cotton, nylon, and/or polyester fibers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of provisional applicationNo. 60/203558, field May 11, 2000, the disclosure of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method for making a heat-resistantelastic article and a heat-resistant elastic article. The inventionespecially relates to a method of making elastic fibers and polymericelastic fibers wherein the elastic fibers are capable of withstandingdyeing and heat-setting processes that typically are conducted atelevated temperatures (such as 110-230° C. and especially at greaterthan or equal to 130° C. for minutes). The inventive method comprisesradiation crosslinking an article (or plurality of articles) under aninert or oxygen limited atmosphere (for example, in N₂, argon, helium,carbon dioxide, xenon and/or a vacuum) wherein the article (or articles)comprises at least one amine stabilizer and preferably another optionalstabilizer additive. More preferably, the radiation crosslinking isperformed at a low temperature (−50 to 40° C.). The elastic article (orarticles) comprises a homogeneously branched ethylene interpolymer(preferably a substantially linear ethylene interpolymer), asubstantially hydrogenated block polymer, or a combination of the two.The heat-resistant elastic articles (especially fibers) are useful invarious durable or repeated-use fabric applications such as, but notlimited to, clothing, under-garments, and sports apparel. Theheat-resistant elastic fibers can be conveniently formed into fabricsusing well-known techniques such as, for example, by using co-knittingtechniques with cotton, nylon, and/or polyester fibers.

BACKGROUND OF THE INVENTION

Disposable articles are typically elastic composite materials preparedfrom a combination of polymer film, fibers, sheets and absorbentmaterials as well as a combination of fabrication technologies. Whereasthe fibers are prepared by well known processes such as spun bonding,melt blowing, melt spinning and continuous filament wounding techniques,the film and sheet forming processes typically involve known extrusionand coextrusion techniques, for example, blown film, cast film, profileextrusion, injection molding, extrusion coating, and extrusion sheeting.

A material is typically characterized as elastic where it has a highpercent elastic recovery (that is, a low percent permanent set) afterapplication of a biasing force. Ideally, elastic materials arecharacterized by a combination of three important properties, that is, alow percent permanent set, a low stress or load at strain, and a lowpercent stress or load relaxation. That is, there should be (1) a lowstress or load requirement to stretch the material, (2) no or lowrelaxing of the stress or unloading once the material is stretched, and(3) complete or high recovery to original dimensions after thestretching, biasing or straining is discontinued.

To be used in the durable fabrics, the fibers making up the fabric haveto be, inter alia, stable during dyeing and heat setting processes. Wefound that the polyolefinic fibers that were irradiated in air tended tofuse together when subjected to the high temperatures typical of dyeingprocesses (about 120° C. for 30 min). Conversely, we surprisingly andunexpectedly found that when irradiated under an inert atmosphere,resultant crosslinked fibers were highly 25 stable during the dyeingprocess (that is, the fibers did not melt or fuse together). Theaddition of a mixture of hindered phenol and hindered amine stabilizersfurther stabilized the fibers at heat setting condition (200-210° C.).

Block polymers generally are elastomeric materials that exhibitexcellent solid-state elastic performance attributes. But unsaturatedblock polymers such as, for example, styrene-butadiene-styrene triblockpolymers, tend to exhibit mediocre thermal stability, especially in themolten state and poor UV stability.

Conversely, known partially hydrogenated (or partially saturated)styrene block copolymers (for example, KRATON G block copolymerssupplied by Shell Chemical Company) are difficult to melt process anddraw into fibers or films. In fact, preparation of fine denier fiber(that is, less than or equal to 40 denier) or thin film (that is, lessthan or equal to 2 mils) from partially hydrogenated or partiallysaturated block polymers is generally not possible at commercialfabrication rates. To overcome characteristic melt processing anddrawing difficulties, partially hydrogenated block copolymers arecommonly formulated with various additives such as oils, waxes andtackifiers. But in order to achieve good melt processability anddrawability, very high levels of low molecular weight additives aretypically required which tend to compromise strength and elasticproperties.

Lycra™ (trademark of Dupont Chemical Company), a segmented polyurethaneelastic material, is currently used in various durable fabrics. But ashortcoming of Lycra is that it is not stable at typical high heatsetting temperatures for PET fiber (200-210° C.). Similar to ordinaryuncrosslinked polyolefin-based elastic materials, Lycra articles tend tolose their integrity and shape and elastic properties when subjected toelevated service temperatures. As such, Lycra can not be successful usedin co-knitting applications with high temperature fibers such aspolyester fibers. Another major shortcoming of Lycra is its cost. Thatis, Lycra tends to be extremely cost prohibitive for many ofapplications.

WO 99/63021, the disclosure of which is incorporated herein byreference, describes elastic articles comprised of a substantiallycured, irradiated, or crosslinked (or curable, irradiated orcrosslinkable) homogeneously branched ethylene interpolymercharacterized as having a density less than 0.90 g/cm³ and containing atleast one nitrogen-containing stabilizer. The described elastic articlesare disclosed as suitable for use in applications where good elasticitymust be maintained at elevated temperatures and after laundering suchas, for example, elastic waist bands of undergarments and otherclothing. WO 99/63021 alsogenerally teaches that the nitrogen-containingstabilizer can be used in combination with phenolic and phosphitestabilizers and reported examples therein are known to include acombination of amine, phenol and phosphorus-containing stabilizers. Butthere is no description of crosslinking or irradiation under an inert orreduced oxygen atmosphere and there is no specific teaching of improvedheat-setting and high temperature dyeing performance.

U.S. Pat. No. 5,324,576, the disclosure of which is incorporated hereinby reference, discloses an elastic nonwoven web of microfibers ofradiation crosslinked ethylene/alpha olefin copolymers, wherein asubstantially linear ethylene polymer (that is, INSITE technologypolymer XUR-1567-48562-9D from The Dow Chemical Company) is set forth inthe reported inventive example. The substantially linear ethylenepolymer is subjected to electron beam radiation in a nitrogen inertedchamber at an oxygen level of approximately 5 ppm. While thesubstantially linear ethylene polymer is known to contain 500 ppm of aphenolic antioxidant, there is no teaching to add a nitrogen-containingstabilizer to the polymer. Moreover, there is no disclosure regardingthe elastic performance of the radiated substantially linear ethylenepolymer at elevated temperatures.

Chemical abstract N1993:235832 (D. W. Woods and I. M. Ward, Plast.,Rubber Comps. Process. Appl. (1992), 18(4), 255-61), the disclosure ofwhich is incorporated herein by reference, describes the use ofradiation under nitrogen to crosslink HDPE fiber to improve creepresistance.

WO 99/60060, the disclosure of which is incorporated herein byreference, discloses heat resistant elastic fiber comprised ofpolyolefinic elastomers made using single site catalyst.

Elastic materials such as films, strips, coating, ribbons and sheetcomprising at least one substantially linear ethylene polymer aredisclosed in U.S. Pat. No. 5,472,775 to Obijeski et al., the disclosureof which is incorporated herein by reference. But Obijeski et al. do notdisclose the performance of their elastic materials at elevatedtemperatures (that is, at temperatures above room temperature).

WO 94/25647, the disclosure of which is incorporated herein byreference, discloses elastic fibers and fabrics made from homogeneouslybranched substantially linear ethylene polymers. The fibers are said toposses at least 50 percent recovery (that is, less than or equal 50percent permanent set) at 100 percent strain. However, there is nodisclosure in WO 94/25647 regarding the elasticity of these fibers atelevated temperatures or the effects of laundering on these fibers.

WO 95/29197, the disclosure of which is incorporated herein byreference, discloses curable, silane-grafted substantially ethylenepolymers which are useful in wire and cable coatings, weather-stripping,and fibers. In the Examples, inventive samples include fibers comprisingsilane-grafted substantially ethylene polymers having densities of 0.868g/cm³ and 0.870 g/cm³. The inventive examples are shown to exhibitimproved elastic recovery at elevated temperatures.

U.S. Pat. No. 5,525,257 to Kurtz et al., the disclosure of which isincorporated herein by reference, discloses that low levels ofirradiation of less than 2 megarads of Ziegler catalyzed linear lowdensity ethylene polymer results in improved stretchability and bubblestability without measurable gelation. Kurtz et al. do not provide anydisclosure regarding elasticity at elevated temperatures.

U.S. Pat. No. 4,957,790 to Warren, the disclosure of which isincorporated herein by reference, discloses the use of pro-rad compoundsand irradiation to prepare heat-shrinkable linear low densitypolyethylene films having an increased orientation rate duringfabrication. In the examples provided therein, Warren employs Zieglercatalyzed ethylene polymers having densities greater than or equal to0.905 g/cm³.

Various compounds are disclosed in the art and/or sold commercially ashigh temperature stabilizers and antioxidants. However, the criteriaemployed to distinguish these compounds as stabilizers and antioxidantstypically relates to their ability to resistance yellowing, crosslinkingand/or the ill-effects of irradiation (for example, gamma irradiationfor purposes of sterilization).

In other instances, different types of stabilizers are equated to oneanother or are said to perform comparably. For example, it is known thathindered phenolic stabilizers (for example, lrganox® 1010 supplied byCiba-Geigy) can be as effective as hindered amine stabilizers (forexample, Chimassorb® 944 supplied by Ciba-Geigy), and vice versa. In aproduct brochure entitled, “Chimassorb 944FL: Hindered Amine LightStabilizer Use and Handling”, printed 1996, Ciba-Geigy states Chimassorb944 “gives long-term heat stability to polyolefins by a radical trappingmechanism similar to that of hindered phenols.”

Further, there is some belief that there is no universally effectivestabilizer for polymers as the definition for stability inevitablyvaries with each application. In particular, there is no effectivestabilizer for washable, high temperature serviceable polyolefinicelastic materials.

In general, stabilizers are known to inhibit crosslinking. In regard tocrosslinking generally, there are several disclosures relating toradiation resistant (for example, gamma and electron beam) polymercompositions comprising amine stabilizers. Such disclosures typicallyteach relatively high levels of amine stabilizer (for example, greaterthan or equal to 0.34 weight percent) are required where inhibition ofcrosslinking, discoloration and other undesirable irradiation effectsare desired. Another examples include stabilized disposal nonwovenfabrics (see, for example, U.S. Pat. No. 5,200,443, the disclosure ofwhich is incorporated herein by reference) and stabilized moldingmaterials (for example, syringes). Gamma sterilization resistant fibers,including amine coatings and the use of hybrid phenolic/aminestabilizers are also known. See, for example, U.S. Pat. No. 5,122,593 toJennings et al., the disclosure of which is incorporated herein byreference.

Stabilized polyethylene compositions with improved resistance tooxidation and improved radiation efficiency are also known. M. Iring etal. in “The Effect of the Processing Steps on the Oxidative Stability ofPolyethylene Tubing Crosslinked by Irradiation”, Die Angew. Makromol.Chemie, Vol. 247, pp. 225-238 (1997), the disclosure of which isincorporated herein by reference, teach that amine stabilizers are moreeffective towards inhibiting electron-beam irradiation effects (that is,provide better resistance against oxidation) than hindered phenols.

WO 92/19993 and U.S. Pat. No. 5,283,101, the disclosures of which areincorporated herein by reference, discloses launderable retroreflectiveappliques comprised of a multicomponent binder composition consisting ofan electron-beam curable elastomer, crosslinker(s), and couplingagent(s) and optional colorants, stabilizers, flame retardants and flowmodifiers. The allegedly inventive appliques are said to be capable ofwithstanding ordinary household washing conditions as well as morestringent industrial washings without loss of retroreflectiveness.Illustrative examples of electron-beam curable elastomers of the binderare said to be “chlorosulfonated polyethylenes, ethylene copolymerscomprising at least about 70 weight percent of polyethylene such asethylene/vinyl acetate, ethylene/acrylate, and ethylene/acrylic acid,and poly(ethylene-co-propylene-co-diene) (“EPDM”) polymers.” Optionalstabilizers are described to be “thermal stabilizers and antioxidantssuch as hindered phenols and light stabilizers such as hindered aminesor ultraviolet stabilizers”. Although there is an equating of thesuitability or effectiveness of hindered phenols to hindered amines inthe descriptions of WO 92/19993 and U.S. Pat. No. 5,283,101, nostabilizer of any kind is exemplified in the provided examples. Further,although the applique can employ polymers that are described as “highlyflexible” before and after electron-beam curing, neither the selectedpolymers nor the applique itself are described as “elastic”. Whileelastic materials typically have a high degree of flexibility (that is,Young's Modulus of less than 10,000 psi (68.9 MPa) where lower modulusmeans more flexibility), highly flexible materials can be nonelastic asthe terms “nonelastic” and “elastic” are defined herein below. That is,not all “highly flexible” materials are elastic.

Although there is an abundance of art related to elastic materialscomprising curable, radiated and/or crosslinked ethylene polymers, andthere is also an abundance of art related to stabilized ethylene polymercompositions and articles, there is no known disclosure of apolyolefinic elastic material with effective additive stabilizationwherein the stabilization does not inhibit the desirable effects ofirradiation and/or crosslinking (that is, impart elevated temperatureelasticity) and yet does inhibit the loss-of elastic integrity (that is,scission) when the material is subjected to processing or finishingsteps at elevated temperatures.

Further, in a product brochure entitled, “Stabilization of Adhesives andTheir Components”, pp. 8-9 (1994), Ciba-Geigy, a premier stabilizersupplier, states that scission occurring in elastomeric materials(forexample, styrene-isoprene-styrene block copolymers) at elevatedtemperatures above 70° C. is not readily controlled by the use ofantioxidants.

As such, there is a present need for cost-effective, stable elasticarticles having good elasticity at elevated temperatures as well as goodheat setting characteristics. That is, there is a need for elasticarticles which in-service retain their shapes under strain at elevatedtemperatures (for example, greater than or equal to 125° C.) and can beprocessed, finished and/or laundered at even higher temperatures andstill retain their in-service elastic characteristics. There is also aneed for a method of making elastic articles having good elasticity atelevated temperatures as well as good dyeing and heat settingcharacteristics. We have discovered that these and other objects can becompletely met by the invention herein described.

SUMMARY OF THE INVENTION

We surprisingly discovered that the combination of radiation under aninert atmosphere or oxygen-reduced atmosphere (that is, less than 20ppm, preferably less than 10 ppm, more preferably less than 5 ppmoxygen) and the use of an amine stabilizer such as a hindered amine oraromatic amine (and optionally a hindered phenol and/or aphosphorus-containing stabilizer) can provide elastic materials(especially fibers) that maintain their elasticity, yet are sufficientlycrosslinked to confer sufficient heat resistance to permit hightemperature dyeing and heat setting. The broad aspect of the inventionis a method of making an elastic article having improved heat resistance(that is, a heat-resistant elastic article) comprising the steps of:

(a) providing at least one elastic polymer or elastic polymercomposition (for example, a homogeneously branched ethylene interpolymerhaving a density of less than or equal to 0.90 g/cm³ at 23° C. or asubstantially hydrogenated block copolymer) which contains at least oneamine or nitrogen-containing stabilizer therein,

(b) fabricating, forming or shaping the polymer or polymer compositioninto an article, and

(c) during or after the fabrication, forming or shaping, subjecting thearticle to ionizing radiation while the article is in or under an inertor oxygen-reduced atmosphere.

Preferably, the irradiation or crosslinking is effectuated usingionizing radiation, most preferably by using electron beam irradiation.Also, preferably, the article (for example, but not limited to, theextrudate, filament, web, film or part) is permitted to cool or isquenched to ambient temperature (that is, permitted to substantiallysolidify) after fabrication or formation before the application ofionizing radiation to effectuate irradiation or crosslinking. Mostpreferably, the irradiation is conducted at a low temperature.

An important benefit of the inventive fibers is now elastic fibers canbe used in combination with fibers which require heat setting atelevated temperatures such as, for example, that PET fibers.

DETAILED DESCRIPTION OF THE INVENTION

The term “heat resistant” as used herein refers to the ability of anelastic polymer or elastic polymer composition in the form of fiber topass the high temperature heat setting and dyeing tests describedherein.

The term “elastic article” is used in reference to shaped items, whilethe term “elastic material” is a general reference to polymer, polymerblends, polymer compositions, articles, parts or items.

The term “elastic” or “elastic-like behavior” as used herein refers toany material (for example, bands, ribbons, strips, tapes, profile,moldings, sheets, coatings, films, threads, filament, fibers, fibrouswebs, fabrics and the like as well as laminates or composites includingthe same) having a permanent set less than or equal to 80 percent,especially less than or equal to 60 percent, more especially less thanor equal to 50 percent and most especially less than or equal 25 percent(that is, most especially greater than or equal to 87.5 percentrecovery) at 200 percent strain and at a temperature between its glasstransition temperature and its crystalline melting point or range isstretchable to a stretched, biased length at least 200 percent greaterthan its relaxed, unstretched length. The extent that a material doesnot return to its original dimensions after being stretched is itspercent permanent set.

Elastic polymeric materials and elastic polymer compositions are alsoreferred to in the art as “elastomers” and “elastomeric”. Preferredelastic shaped articles are fibers and films, and especially preferredarticles of the invention are fibers and fabrics containing the fibers.

The term “nonelastic or inelastic” as used herein means the material orarticle is not elastic as defined herein (that is, the material orarticle has a percent permanent set greater than 80 at 200 percentstrain).

The term “meltblown” is used herein in the conventional sense to referto fibers formed by extruding the molten elastic polymer or elasticpolymer composition through a plurality of fine, usually circular, diecapillaries as molten threads or filaments into converging high velocitygas streams (for example, air) which function to attenuate the threadsor filaments to reduced diameters. Thereafter, the filaments or threadsare carried by the high velocity gas streams and deposited on acollecting surface to form a web of randomly dispersed fibers withaverage diameters generally smaller than 10 microns.

The term “spunbond” is used herein in the conventional sense to refer tofibers formed by extruding the molten elastic polymer or elastic polymercomposition as filaments through a plurality of fine, usually circular,die capillaries of a spinneret with the diameter of the extrudedfilaments then being rapidly reduced and thereafter depositing thefilaments onto a collecting surface to form a web of randomly dispersedspunbond fibers with average diameters generally between about 7 andabout 30 microns.

The term “nonwoven” as used herein and in the conventional sense means aweb or fabric having a structure of individual fibers or threads whichare randomly interlaid, but not in an identifiable manner as is the casefor a knitted fabric. The elastic fiber of the present invention can beemployed to prepare inventive nonwoven elastic fabrics as well ascomposite structures comprising the elastic nonwoven fabric incombination with nonelastic materials.

The term “conjugated” refers to fibers which have been formed from atleast two polymers extruded from separate extruders but meltblown orspun together to form one fiber. Conjugated fibers are sometimesreferred to in the art as multicomponent or bicomponent fibers. Thepolymers are usually different from each other although conjugatedfibers may be monocomponent fibers. The polymers are arranged insubstantially constantly positioned distinct zones across thecross-section of the conjugated fibers and extend continuously along thelength of the conjugated fibers. The configuration of conjugated fiberscan be, for example, a sheath/core arrangement (wherein one polymer issurrounded by another), a side by side arrangement, a pie arrangement oran “islands-in-the sea” arrangement. Conjugated fibers are described inU.S Pat. No. 5,108,820 to Kaneko et al.; U.S. Pat. No. 5,336,552 toStrack et al.; and U.S. Pat. No. 5,382,400 to Pike et al., thedisclosures of all of which are incorporated herein by reference. Theelastic fiber of the present invention can be in a conjugatedconfiguration, for example, as a core or sheath, or both.

The term “thermal bonding” is used herein refers to the heating offibers to effect the melting (or softening) and fusing of fibers suchthat a nonwoven fabric is produced. Thermal bonding includes calendarbonding and through-air bonding as well as methods known in the art.

The expression “thermal bondable at a reduced hot melt adhesive amount”refers to comparative peel test results using A to Findley AdhesiveHX9275 (supplied by Ato Findley Nederlands B. V., Roosendaal, TheNetherlands) or H. B. Fuller Adhesive D875BD1 (supplied by H. B. FullerGmbH, I-Oneburg, Germany) and test procedures and methods described inWO 00/00229, the disclosure of which is incorporated herein byreference, wherein the same peel strength as the adhesive withoutdeploying thermal bonding can be obtained even though the quantity ofadhesive is at least 15 percent less where thermal bonding is deployed.

The term “polymer”, as used herein, refers to a polymeric compoundprepared by polymerizing one or more monomers. As used herein, genericterm “polymer” embraces the terms “homopolymer,” “copolymer,”“terpolymer” as well as “interpolymer.” A polymer is usually made in onereactor or polymerization vessel but can as well as be made usingmultiple reactors or polymerization vessels, although the latter isusually referred to as a polymer composition.

The term “polymer composition” as used herein refers to a mixture of apolymer and at least one ingredient added to or mixed with the polymerafter the polymer is formed. Thus, the term “polymer composition”includes poly-blends (that is, admixtures of two or more polymerswherein each polymers is made in separate reactors or polymerizationwhether or not the reactors or vessels are part of the samepolymerization system or not).

The term “interpolymer”, as used herein refers to polymers prepared bythe polymerization of at least two different types of monomers. As usedherein the generic term “interpolymer” includes the term “copolymers”(which is usually employed to refer to polymers prepared from twodifferent monomers) as well as the term “terpolymers” (which is usuallyemployed to refer to polymers prepared from three different types ofmonomers).

The term “radiated” or “irradiated” as used herein means the elasticpolymer or elastic polymer composition or the shaped article comprisedof the elastic polymer or elastic polymer composition was subjected toat least 3 megarads (or the equivalent thereof) of radiation dosagewhether or not there was a measurable decrease in percent xyleneextractables (that is, increase in insoluble gel). That is, substantialcrosslinking may not result from the irradiation.

The terms “crosslinked” and “substantially crosslinked” as used hereinmean the elastic polymer or elastic polymer composition or the shapedarticle comprised of the elastic polymer or elastic polymer compositionis characterized as having xylene extractables of less than or equal to45 weight percent (that is, greater than or equal to 55 weight percentgel content), preferably less than or equal to 40 weight percent (thatis, greater than or equal to 60 weight percent gel content), morepreferably less than or equal to 35 weight percent (that is, greaterthan or equal to 65 weight percent gel content), where xyleneextractables (and gel content) are determined in accordance with ASTMD-2765.

The terms “cured” and “substantially cured” as used herein means theelastic polymer or elastic polymer composition or the shaped articlecomprised of the elastic polymer or elastic polymer composition wassubjected or exposed to a treatment which induced crosslinking. As usedherein, the terms relate to the use of a grafted silane compound.

The terms “curable” and “crosslinkable” as used herein mean the elasticpolymer or elastic polymer composition or the shaped article comprisedof the elastic polymer or elastic polymer composition is not crosslinkedand has not been subjected or exposed to treatment which inducescrosslinking although the elastic polymer, elastic polymer compositionor the shaped article comprised of the elastic polymer or elasticpolymer composition comprises additive(s) or functionality that willeffectuate crosslinking upon subjected or exposed to such treatment.

The term “pro-rad additive” as used herein means a compound which is notactivated during normal fabrication or processing of the elastic polymeror elastic polymer composition, but can be activated by the applicationof temperatures (heat) substantially above normal fabrication orprocessing temperatures or ionizing energy (or both) (and especiallywith regard to article, part or item fabrication and processing) toeffectuate some measurable gelation or preferably, substantialcrosslinking.

In the practice of the present invention, curing, irradiation orcrosslinking of the elastic polymers, elastic polymer compositions orarticles comprising elastic polymers or elastic polymer compositions canbe accomplished by any means known in the art, including, but notlimited to, electron-beam irradiation, beta irradiation, X-rays, gammairradiation, controlled thermal heating, corona irradiation, peroxides,allyl compounds and UV radiation with or without crosslinking catalyst.Electron-beam irradiation is the preferred technique for crosslinkingthe substantially hydrogenated block polymer or the shaped articlecomprised of the substantially hydrogenated block polymer. Preferably,the curing, irradiation, crosslinking or combination thereof provides apercent gel, as determined using xylene in accordance with ASTM D-2765,of greater than or equal to 40 weight percent, more preferably greaterthan or equal to 50 weight percent, most preferably greater than orequal to 70 weight percent.

Suitable electron-beam irradiation equipment is available from EnergyServices, Inc. Wilmington, Mass. with capabilities of at least 100kilo-electron volts (KeV) and at least 5 kilowatts (Kw). Preferably,electrons are employed up to 70 megarads dosages. The irradiation sourcecan be any electron beam generator operating in a range of about 150 Kevto about 12 mega-electron volts (MeV) with a power output capable ofsupplying the desired dosage. The electron voltage can be adjusted toappropriate levels which may be, for example, 100,000, 300,000,1,000,000 or 2,000,000 or 3,000,000 or 6,000,000 or higher or lower.Many other apparati for irradiating polymeric materials are known in theart.

In the present invention, effective irradiation is usually carried outat a dosage between about 3 megarads (Mrad) to about 35 megarads,preferably from about 10 to about 35 megarads, more preferably fromabout 15 to about 32 megarads, and most preferably from about 19 toabout 28 megarads. Further, the irradiation can be conveniently carriedout at room temperature. But preferably, irradiation is conducted whilethe article (or plurality of articles) is at lower temperaturesthroughout the exposure, such as, for example, at about −50° C. to about40° C., especially at about −20° C. to about 30° C., more especially atabout 0C to about 25° C., and most especially from about 0° C. to about12° C.

The irradiation can be carried out on-line (that is, during fabricationof the article), off-line (such as after fabrication of the article, forexample, film, by unwinding or wrapping the fabricated article) oron-spool (as such in the case of fibers, filaments and the like).Preferably, the irradiation is carried out after shaping or fabricationof the article. Also, in a preferred embodiment, a pro-rad additive isincorporated into the elastic polymer or elastic polymer composition andthe polymer or composition is subsequently irradiated with electron beamradiation at about 8 to about 32 megarads.

In another aspect of the invention, the irradiation (preferably electronbeam irradiation) is carried out under an inert or oxygen-limitedatmosphere. Suitable atmospheres can be provided by the use of helium,argon, nitrogen, carbon dioxide, xenon and/or a vacuum. Substantialimprovements in high temperature serviceability can be gained by usingan inert or oxygen-limited atmosphere without any attendant substantiallost in elastic performance ordinarily associated with service or use atelevated temperatures.

Crosslinking can be promoted with a crosslinking catalyst, and anycatalyst that will provide this function can be used. Suitable catalystsgenerally include organic bases, carboxylic acids, and organometalliccompounds including organic titanates and complexes or carboxylates oflead, cobalt, iron, nickel, zinc and tin. Dibutyltindilaurate,dioctyltinmaleate, dibutyltindiacetate, dibutyltindioctoate, stannousacetate, stannous octoate, lead naphthenate, zinc caprylate, cobaltnaphthenate; and the like. Tin carboxylate, especiallydibutyltindilaurate and dioctyltinmaleate, are particularly effectivefor this invention. The catalyst (or mixture of catalysts) is present ina catalytic amount, typically between about 0.015 and about 0.035 phr.

Representative pro-rad additives include, but are not limited to, azocompounds, organic peroxides and polyfunctional vinyl or allyl compoundssuch as, for example, triallyl cyanurate, triallyl isocyanurate,pentaerthritol tetramethacrylate, glutaraldehyde, ethylene glycoldimethacrylate, diallyl maleate, dipropargyl maleate, dipropargylmonoallyl cyanurate, dicumyl peroxide, di-tert-butyl peroxide, t-butylperbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate,methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane,lauryl peroxide, tert-butyl peracetate, azobis isobutyl nitrite and thelike and combination thereof. Preferred pro-rad additives for use in thepresent invention are compounds which have poly-functional (that is, atleast two) moieties such as C═C, C═N or C═O.

At least one pro-rad additive can be introduced to the ethyleneinterpolymer by any method known in the art. However, preferably thepro-rad additive(s) is introduced via a masterbatch concentratecomprising the same or different base resin as the ethyleneinterpolymer. Preferably, the pro-rad additive concentration for themasterbatch is relatively high for example, greater than or equal to 25weight percent (based on the total weight of the concentrate).

The at least one pro-rad additive is introduced to the ethylene polymerin any effective amount. Preferably, the at least one pro-rad additiveintroduction amount is from about 0.001 to about 5 weight percent, morepreferably from about 0.005 to about 2.5 weight percent and mostpreferably from about 0.015 to about 1 weight percent (based on thetotal weight of the substantially hydrogenated block polymer).

Amine or Nitrogen-Containing Stabilizer

Suitable amine or nitrogen-containing stabilizers for use in the presentinvention include, but are not limited to, naphthylamines (for example,N-phenyl naphthylamines such as Naugard PAN supplied by Uniroyal);diphenylamine and derivatives thereof which are also referred to assecondary aromatic amines (for example, 4,4′-bis(∝,∝-dimethylbenzyl)-diphenylamine which is supplied by UniroyalChemical under the designation Naugard® 445); p-phenylenediamines (forexample, Wingstay® 300 supplied by Goodyear); piperidines andderivatives thereof (for example,poly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2, 4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])which is supplied by Ciba Specialty Chemicals under the designation ofChimassorb® 944 as well as other substituted piperidines such asChimassorb® 119, Tinuvin® 622 and Tinuvine® 770, all three also suppliedby Ciba Specialty Chemicals), and quinolines (for example, oxyquinolinesand hydroquinolines such as polymeric2,2,4-trimethyl-1,2-dihydroquinoline which is supplied by VanderbiltCompany under the designation s Agerite® D).

Suitable amine or nitrogen-containing stabilizers also include thehybrid stabilizers such as aminophenols (for example, N,N′-hexamethylenebis-3-(3,5-ditert-butyl-4-hydroxyphenyl)-propionamide),acylaminophenols (which are also referred to as 4-hydroyanilides) andthe various hybrid stabilizers described in U.S. Pat. No. 5,122,593 (thedisclosure of which is incorporated herein by reference) which consistof a N-(substituted)-1-(piperazine-2-one alkyl) group at one end and a(3,5-dialkyl-4-hydroxyphenyl)-α,α-disubstituted acetamine at the otherend.

Other suitable amine or nitrogen-containing stabilizers includecarboxylic acid amides of aromatic mono and dicarboxylic acids andN-monosubstituted derivatives (e.g N,N′-diphenyloxamide and2,2′-oxamidobisethyl 3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionatewhich is supplied by Uniroyal Chemical under the designation Naugard®XL-1); hydrazides of aliphatic and aromatic mono- and dicarboxylic acidsand N-acylated derivatives thereof; bis-acylated hydrazine derivatives;melamine; benzotriazoles, hydrazones; acylated derivatives ofhydrazino-triazines; polyhydrazides; salicylaethylenediimines;salicylaloximes; derivatives of ethylenediamino tetraacetic acid; andaminotriazoles and acylated derivatives thereof.

Preferred amine or nitrogen-containing stabilizers for use in thepresent invention are diphenylamines, substituted piperidines andhydroquinolines. The most preferred amine or nitrogen-containingstabilizers are hindered amines since they tend to cause lessdetrimental polymer discoloration than aromatic amines.

Further, the at least one amine or nitrogen-containing stabilizer can beemployed alone or in combination with one or more other stabilizer suchas, for example, but not limited to, other amine or nitrogen-containingstabilizer; a hindered phenol (for example,2,6-di-tert-butyl-4-methylphenol which is supplied by Koppers Chemicalunder the designation BHT®; tetrakis(methylene3-(3,5-di-tert-butyl-4-hydro xyphenyl) propionate) methane which issupplied by Ciba Specialty Chemicals under the designation Irganox®1010; Irganox 1076 supplied by Ciba Specialty Chemicals; Cyanox 1790which is tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-(1H,3H,5H)-trione as supplied byCytec; and Irganox 3114 which is1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazinane-2,4,6-trioneas supplied by Ciba Specialty Chemicals); a thioester (for example,dilauryl thiodipropionate which is supplied by Evans under thedesignation Evanstab® 12); a phosphite (for example, Irgafos® 168supplied by Ciba Specialty Chemicals and tri(nonylphenyl) phosphitewhich is supplied by Uniroyal Chemical under the designation Naugard®P); diphosphite (for example, distearyl pentaerthritol diphosphite whichis supplied by Borg-Warner under the designation Weston® 618); apolymeric phosphite (for example, Wytox® 345-S(1) supplied by Olin);phosphited phenol and bisphenol (for example, Wytox® 604 supplied byOlin); and diphosphonite (for example, tetrakis(2,4-di-tert-butylphenyl)4,4′-biphenylylene diphosphonite which is supplied by Sandox under thedesignation Sandostab® P-EPQ). A preferred combination is a hinderedamine and a hindered phenol. With regard to hindered phenols, Cyanox1790 and Irganox 3114 preferred since these stabilizers tend to have aless detrimental effects on discoloration (due to nitroxide gasformation) than Irganox 1076 or Irganox 1010.

Preferably, the at least one amine or nitrogen-containing stabilizer(and optional other stabilizer) is added to the homogeneously branchedethylene polymer or the substantially hydrogenated block polymer or bothin a melt compounding step, more preferably by the use of an additiveconcentrate, prior to fabrication and shaping process steps. The atleast one nitrogen-containing stabilizer (and the optional otherstabilizer) can be added to the interpolymer or block polymer at anyeffective concentration. But, preferably, the total stabilizerconcentration is in the range of from about 0.02 to about 2 weightpercent (based on the total weight of the stabilizer and interpolymerand/or block polymer), more preferably in the range from about 0.075 toabout 1 weight percent (based on the total weight of the stabilizer andthe interpolymer and/or block polymer) and most preferably in the rangeof from about 0.1 to about 0.32 weight percent (based on the totalweight of the stabilizer and the interpolymer and/or block). Where anoptional other stabilizer is used (for example, a hindered phenol), theconcentration of the amine to the phenol is in the range from about 2:1to about 1:2, preferably in the range of from about 1.25:1 to about1:1.25.

An especially preferred embodiment is a combination of amine with aphenol and a phosphorus-containing stabilizer, more preferably where thetotal concentration of the phenol and a phosphorus-containing stabilizeris less than or equal to 0.15 weight percent and the amine ornitrogen-containing stabilizer concentration is in the range of 0.15 to0.32 weight percent.

In-process additives, for example, calcium stearate, water, andfluoropolymers, may also be used for purposes such as for thedeactivation of residual catalyst or improved processability or both.Colorants, coupling agents and fire retardants may also be include aslonger as their incorporation does not disturb the desirablecharacteristics of the invention.

Suitable polymers for use in the present invention includeethylene-alpha olefin interpolymers, substantially hydrogenated blockpolymers, styrene butadiene styrene block polymers,styrene-ethylene/butene-styrene block polymers, ethylene styreneinterpolymers, polypropylenes, polyamides, polyurethanes and anycombination thereof. But preferred polymers are substantiallyhydrogenated block polymers and homogeneously branched ethylene-alphaolefin interpolymers.

Substantially Hydrogenated Block Polymer

The term “substantially hydrogenated block polymer” as used herein meansa block copolymer that is characterized as having a hydrogenation levelof greater than 90 percent (by number) for each vinyl aromatic monomerunit block and a hydrogenation level of greater than 95 percent (bynumber) for each conjugated diene polymer block, where for both thevinyl aromatic monomer and conjugated diene monomer repeating unitblocks, hydrogenation converts unsaturated moieties into saturatedmoieties.

The term “partially hydrogenated block polymer” as used herein means ablock polymer that is hydrogenated but does not meet the hydrogenationlevels that define a substantially hydrogenated block polymer.

Substantially hydrogenated block copolymers comprise at least onedistinct block of a hydrogenated polymerized vinyl aromatic monomer andat least one block of a hydrogenated polymerized conjugated dienemonomer. Preferred substantially hydrogenated block polymers aretriblock comprising (before hydrogenation) two vinyl aromatic monomerunit blocks and one conjugated diene monomer unit block. Suitablesubstantially hydrogenated block polymers for use in the presentinvention are generally characterized by:

a) a weight ratio of conjugated diene monomer unit block to vinylaromatic monomer unit block before hydrogenation of greater than 60:40

b) a weight average molecular weight (M_(w)) before hydrogenation offrom about 30,000 to about 150,000 (preferably, especially for highdrawdown application such as, for example, fiber spinning, less than orequal to 81,000), wherein each vinyl aromatic monomer unit block (A) hasa weight average molecular weight, Mw_(a), of from about 5,000 to about45,000 and each conjugated diene monomer unit block (B) has a weightaverage molecular weight, Mw_(b), of from about 12,000 to about 110,000;and

c) a hydrogenation level such that each vinyl aromatic monomer unitblock is hydrogenated to a level of greater than 90 percent and eachconjugated diene monomer unit block is hydrogenated to a level ofgreater than 95 percent, as determined using UV-VIS spectrophotometryand proton NMR analysis.

Neat substantially hydrogenated block polymers can be furthercharacterized as having a viscosity at 0.1 rad/sec and 190° C., asdetermined using a parallel plate rheometer (Rheometrics RMS-800equipped with 25 mm diameter flat plates at 1.5 mm gap under a nitrogenpurge), that is less than 1,000,000 poises, preferably less than orequal to 750,000 poises, more preferably less than 500,000 poises orthat is at least 30 percent, preferably at least 50 percent, morepreferably at least 80 lower than that of a partially hydrogenated blockpolymer having the same monomer types, number of monomer units, symmetryand weight average molecular weight, or that is defined by the followinginequality:

Ln viscosity at 0.1 rad/sec≦(7.08×10⁵)(M _(w))+7.89

where “Ln” means natural log and “≦” means less than or equal to.

Neat substantially hydrogenated block polymers can also be furthercharacterized as having a drawability of less than or equal to 200denier, preferably less than or equal to 175 denier, more preferablyless than or equal to 50 denier when fiber spun at 0.43 g/minute and250° C. using an Instron capillary rheometer equipped with a die havinga 1,000 micron diameter and a 20:1 L/D. The term “neat” is used hereinto mean unblended with other synthetic polymer.

The vinyl aromatic monomer is typically a monomer of the formula:

wherein R′ is hydrogen or alkyl, Ar is phenyl, halophenyl, alkylphenyl,alkylhalophenyl, naphthyl, pyridinyl, or anthracenyl, wherein any alkylgroup contains 1 to 6 carbon atoms which may be mono or multisubstitutedwith functional groups such as halo, nitro, amino, hydroxy, cyano,carbonyl and carboxyl. More preferably Ar is phenyl or alkyl phenyl withphenyl being most preferred. Typical vinyl aromatic monomers includestyrene, alpha-methylstyrene, all isomers of vinyl toluene, especiallypara-vinyl toluene, all isomers of ethyl styrene, propyl styrene, butylstyrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene andmixtures thereof. The block copolymer can contain more than one specificpolymerized vinyl aromatic monomer. In other words, the block copolymercan contain a polystyrene block and a poly-alpha-methylstyrene block.The hydrogenated vinyl aromatic block may also be a copolymer, whereinthe hydrogenated vinyl aromatic portion is at least 50 weight percent ofthe copolymer.

The conjugated diene monomer can be any monomer having 2 conjugateddouble bonds. Such monomers include for example 1,3-butadiene,2-methyl-1,3-butadiene, 2-methyl-1,3 pentadiene, isoprene and similarcompounds, and mixtures thereof. The block copolymer can contain morethan one specific polymerized conjugated diene monomer. In other words,the block copolymer can contain a polybutadiene block and a polyisopreneblock.

The conjugated diene polymer block can comprise materials that remainamorphous after the hydrogenation process, or materials which arecapable of crystallization after hydrogenation. Hydrogenatedpolyisoprene blocks remain .amorphous, while hydrogenated polybutadieneblocks can be either amorphous or crystallizable depending upon theirstructure. Polybutadiene can contain either a 1,2 configuration, whichhydrogenates to give the equivalent of a 1-butene repeat unit, or a1,4-configuration, which hydrogenates to give the equivalent of anethylene repeat unit. Polybutadiene blocks having at least approximately40 weight percent 1,2-butadiene content, based on the weight of thepolybutadiene block, provides substantially amorphous blocks with lowglass transition temperatures upon hydrogenation. Polybutadiene blockshaving less than approximately 40 weight percent 1,2-butadiene content,based on the weight of the polybutadiene block, provide crystallineblocks upon hydrogenation. Depending on the final application of thepolymer it may be desirable to incorporate a crystalline block (toimprove solvent resistance) or an amorphous, more compliant block. Insome applications, the block copolymer can contain more than oneconjugated diene polymer block, such as a polybutadiene block and apolyisoprene block. The conjugated diene polymer block may also be acopolymer of a conjugated diene, wherein the conjugated diene portion ofthe copolymer is at least 50 weight percent of the copolymer. Theconjugated diene polymer block may also be a copolymer of more than oneconjugated diene, such as a copolymer of butadiene and isoprene. Also,other polymeric blocks may also be included in the substantiallyhydrogenated block polymers used in the present invention.

A “block” is herein defined as a polymeric segment of a copolymer thatexhibits microphase separation from a structurally or compositionallydifferent polymeric segment of the copolymer. Microphase separationoccurs due to the incompatibility of the polymeric segments within theblock copolymer. The separation of block segments can be detected by thepresence of distinct glass transition temperatures. Microphaseseparation and block copolymers are generally discussed in “BlockCopolymers-Designer Soft Materials”, PHYSICS TODAY, February, 1999,pages 32-38, the disclosure of which is incorporated herein byreference.

Suitable substantially hydrogenated block polymers typically have aweight ratio of conjugated diene monomer unit block to vinyl aromaticmonomer unit block before hydrogenation of from about 60:40 to about95:5, preferably from about 65:35 to about 90:10, more preferably fromabout 70:30 to about 85:15, based on the total weight of the conjugateddiene monomer unit and vinyl aromatic monomer unit blocks.

The total weights of the vinyl aromatic monomer unit block(s) and theconjugated diene monomer unit block(s) before hydrogenation is typicallyat least 80 weight percent, preferably at least 90, and more preferablyat least 95 weight percent of the total weight of the hydrogenated blockpolymer. More specifically, the hydrogenated block polymer typicallycontains from 1 to 99 weight percent of a hydrogenated vinyl aromaticpolymer (for example, polyvinylcyclohexane or PVCH block, generally from10, preferably from 15, more preferably from 20, even more preferablyfrom 25, and most preferably from 30 to 90 weight percent, preferably to85 and most preferably to 80 percent, based on the total weight of thehydrogenated block polymer. And, as to the conjugated diene polymerblock, the hydrogenated block copolymer typically contains from 1 to 99weight percent of a hydrogenated conjugated diene polymer block,preferably from 10, more preferably from 15, and most preferably from 20to 90 weight percent, typically to 85, preferably to 80, more preferablyto 75, even more preferably to 70 and most preferably to 65 percent,based on the total weight of the copolymer.

The substantially hydrogenated block polymers suitable for use in thepresent invention are produced by the hydrogenation of block copolymersincluding triblock, multiblock, tapered block, and star block polymerssuch as, for example, but not limited to, SBS, SBSBS, SIS, SISIS, andSISBS (wherein S is polystyrene, B is polybutadiene and I ispolyisoprene). Preferred block polymers contain at least one blocksegment comprised of a vinyl aromatic polymer block, more preferably theblock polymer is symmetrical such as, for example, a triblock with avinyl aromatic polymer block on each end. The block polymers may,however, contain any number of additional blocks, wherein these blocksmay be attached at any point to the triblock polymer backbone. Thus,linear blocks would include, for example, SBS, SBSB, SBSBS, and SBSBSB.That is, suitable block polymers include asymmetrical block polymers andtapered linear block polymers.

The block polymer can also be branched, wherein polymer chains areattached at any point along the polymer backbone. In addition, blends ofany of the aforementioned block copolymers can also be used as well asblends of the block copolymers with their hydrogenated homopolymercounterparts. In other words, a hydrogenated SBS block polymer can beblended with a hydrogenated SBSBS block polymer or a hydrogenatedpolystyrene homopolymer or both. It should be noted here that in theproduction of triblock polymers, small amounts of residual diblockcopolymers are often produced.

The weight average molecular weight (M_(w)) of suitable substantiallyhydrogenated block polymers, as measured before hydrogenation, isgenerally from 30,000, preferably from 45,000, more preferably from55,000 and most preferably from 60,000 to 150,000, typically to 140,000,generally to 135,000, preferably to 130,000, more preferably to 125,000,and most preferably to 120,000. But preferably, especially when usedneat (that is, without being blended with other polymer) for fiber meltspinning purposes, the weight average molecular weight beforehydrogenation will be less than or equal to 81,500, more preferably lessthan or equal to 75,000 and most preferably less than or equal to67,500.

Substantially hydrogenated block polymers can have vinyl aromaticmonomer unit block with weight average molecular weights, Mw, beforehydrogenation of from about 6,000, especially from about 9,000, moreespecially from about 11,000, and most especially from about 12,000 toabout 45,000, especially to about 35,000, more especially to about25,000 and most especially to about 20,000. The weight average molecularweight of the conjugated diene monomer unit block before hydrogenationcan be from about 12,000, especially from about 27,000, more especiallyfrom about 33,000 and most especially from about 36,000 to about110,000, especially to about 100,000, more especially to about 90,000and most especially to about 80,000. But preferably, especially whenused neat for fiber melt spinning purposes, for triblocks comprising twohydrogenated vinyl aromatic monomer unit blocks and one hydrogenatedconjugated diene monomer unit block, the weight average molecular weightof each vinyl aromatic monomer unit block before hydrogenation will beless than or equal to 15,000, more preferably less than or equal to13,000 and most preferably less than or equal to 12,000.

It is important to note that each individual block of the hydrogenatedblock copolymer of the present invention, can have its own distinctmolecular weight. In other words, for example, two vinyl aromaticpolymer blocks may each have a different molecular weight.

M_(p) and M_(w)., as used to throughout the specification, aredetermined using gel permeation chromatography (GPC). The molecularweight of the substantially hydrogenated block polymer and propertiesobtained are dependent upon the molecular weight of each of the monomerunit blocks. For substantially hydrogenated block polymers, molecularweights are determined by comparison to narrow polydispersityhomopolymer standards corresponding to the different monomer unitsegments (for example, polystyrene and polybutadiene standards are usedfor SBS block copolymers) with adjustments based on the composition ofthe block copolymer. Also for example, for a triblock copolymer composedof styrene (S) and butadiene (B), the copolymer molecular weight can beobtained by the following equation:

In Mc=x InMa+(1−x)In Mb

where Mc is the molecular weight of the copolymer, x is the weightfraction of S in the copolymer, Ma is the apparent molecular based onthe calibration for S homopolymer and Mb is the apparent molecularweight based on the calibration for homopolymer B. This method isdescribed in detail by L. H. Tung, Journal of Applied Polymer Science,volume 24,953,1979, the disclosure of which is incorporated herein byreference.

Methods of making block polymers are well known in the art. Typically,block polymers are made by anionic polymerization, examples of which arecited in Anionic Polymerization: Principles and Practical Applications,H. L. Hsieh and R. P. Quirk, Marcel Dekker, New York, 1996, thedisclosure of which is incorporated herein by reference. Block polymerscan be made by sequential monomer addition to a carbanionic initiatorsuch as sec-butyl lithium or n-butyl lithium. Block polymers can also bemade by coupling a triblock material with a divalent coupling agent suchas 1,2-dibromoethane, dichlorodimethylsilane, or phenylbenzoate. In thismethod, a small chain (less than 10 monomer repeat units) of aconjugated diene monomer can be reacted with the vinyl aromatic monomerunit coupling end to facilitate the coupling reaction. Note, however,vinyl aromatic polymer blocks are typically difficult to couple,therefore, this technique is commonly used to achieve coupling of thevinyl aromatic polymer ends. The small chain of the conjugated dienemonomer unit does not constitute a distinct block since no microphaseseparation is achieved.

Coupling reagents and strategies which have been demonstrated for avariety of anionic polymerizations are discussed in Hsieh and Quirk,Chapter 12, pgs. 307-331. In another method, a difunctional anionicinitiator is used to initiate the polymerization from the center of theblock system, wherein subsequent monomer additions add equally to bothends of the growing polymer chain. An example of a such a difunctionalinitiator is 1,3-bis(1-phenylethenyl) benzene treated with organolithiumcompounds, as described in U.S. Pat. Nos. 4,200,718 and 4,196,154, whichare incorporated herein by reference.

After preparation of the block polymer, the polymer is hydrogenated toremove sites of unsaturation in both the conjugated diene monomer unitblock(s) and the vinyl aromatic monomer unit block(s) of the polymer.Any method of hydrogenation can be used where suitable methods typicallyinclude the use of metal catalysts supported on an inorganic substrate,such as Pd on BaSO₄ (U.S. Pat. No. 5,352,744) and Ni on kieselguhr (U.S.Pat. No. 3,333,024), both of which are incorporated herein by reference.Additionally, soluble, homogeneous catalysts such those prepared fromcombinations of transition metal salts of 2-ethylhexanoic acid and alkyllithiums can be used to fully saturate block copolymers, as described inDie Makromolekulare Chemie, Volume 160, pp. 291,1972, the disclosure ofwhich is incorporated herein by reference.

Hydrogenation can also be achieved using hydrogen and a heterogeneouscatalyst such as those described in U.S. Pat. Nos. 5,352,744; 5,612,422and 5,645,253, the disclosures of which are incorporated herein byreference. The catalysts described therein are heterogeneous catalystsconsisting of a metal crystallite supported on a porous silicasubstrate. An example of a silica supported catalyst which is especiallyuseful in the polymer hydrogenation is a silica which has a surface areaof at least 10 m²/g which is synthesized such that is contains poreswith diameters ranging between 3000 and 6000 Angstroms. This silica isthen impregnated with a metal capable of catalyzing hydrogenation of thepolymer, such as nickel, cobalt, rhodium, ruthenium, palladium,platinum, other Group Vill metals, combinations or alloys thereof. Otherheterogeneous catalysts can also be used, having average pore diametersin the range of 500 to 3,000 Angstroms.

The level of hydrogenation of the substantially hydrogenated blockpolymers used in the present invention is greater than 95 percent forthe conjugated diene monomer unit block(s) and greater than 90 percentfor the vinyl aromatic monomer unit block(s), preferably greater than 99percent for the conjugated diene monomer unit block(s) and greater than95 percent for the vinyl aromatic monomer unit block(s), more preferablygreater than 99.5 percent for the conjugated diene monomer unit block(s)and greater than 98 percent for the vinyl aromatic monomer unitblock(s), and most preferably greater than 99.9 percent for theconjugated diene monomer unit block(s) and 99.5 percent for the vinylaromatic monomer unit block(s).

The term “level of hydrogenation” refers to the percentage of theoriginal unsaturated bonds that become saturated upon hydrogenation. Thelevel of hydrogenation for the (hydrogenated) vinyl aromatic monomerunit block(s) can be determined using UV-VIS spectrophotometry, whilethe level of hydrogenation for the (hydrogenated) diene conjugatedmonomer unit block(s) can be determined using proton NMR.

The block polymer composition (that is, ratio of conjugated dienemonomer unit blocks to vinyl aromatic monomer unit blocks) can bedetermined using proton NMR and a comparative integration technique suchas that described by Santee, Chang and Morton in Journal of PolymerScience: Polymer Letter Edition, Vol. 11, page 449 (1973), thedisclosure of which is incorporated herein by reference. Conveniently, aVarian Inova NMR unit set at 300 MHz for ¹H is used and samples of theblock polymer are analyzed as 4 percent solutions (w/v) in CDCI₃(deuterochloroform).

Individual block lengths can be calculated from the weight averagemolecular weight, M_(w), and ¹H NMR compositional analysis and byassuming a symmetrical structure (for example, a triblock with terminalpolystyrene blocks).

Homogeneously Branched Ethylene Interpolymer

The term “homogeneously branched ethylene polymer” is used herein in theconventional sense to refer to an ethylene interpolymer in which thecomonomer is randomly distributed within a given polymer molecule andwherein substantially all of the polymer molecules have the sameethylene to comonomer molar ratio. The term refers to an ethyleneinterpolymer that are manufactured using so-called homogeneous orsingle-site catalyst systems known in the art such Ziegler vanadium,hafnium and zirconium catalyst systems and metallocene catalyst systemsfor example, a constrained geometry catalyst systems which is furtherdescribed herein below.

Homogeneously branched ethylene polymers for use in the presentinvention can be also described as having less than 15 weight percent,preferably less 10 weight percent, more preferably less than 5 and mostpreferably zero (0) weight percent of the polymer with a degree of shortchain branching less than or equal to methyls/1000 carbons. That is, thepolymer contains no measurable high density polymer fraction(forexample, there is no fraction having a density of equal to or greaterthan 0.94 g/cm³), as determined, for example, using a temperature risingelution fractionation (TREF) technique and infrared or 13C nuclearmagnetic resonance (NMR) analysis.

Preferably, the homogeneously branched ethylene polymer is characterizedas having a narrow, essentially single melting TREF profile/curve andessentially lacking a measurable high density polymer portion, asdetermined using a temperature rising elution fractionation technique(abbreviated herein as “TREF”).

The composition distribution of an ethylene interpolymer can be readilydetermined from TREF as described, for example, by Wild et al., Journalof Polymer Science, Poly. Phys. Ed., Vol.20, p. 441 (1982), or in U.S.Pat. Nos. 4,798,081; 5,008,204; or by L. D. Cady, “The Role of ComonomerType and Distribution in LLDPE Product Performance,” SPE RegionalTechnical Conference, Quaker Square Hilton, Akron, Ohio, October 1-2,pp.107-119 (1985), the disclosures of all which are incorporated hereinby reference.

The composition (monomer) distribution of the interpolymer can also bedetermined using ¹³C NMR analysis in accordance with techniquesdescribed in U.S. Pat. No. 5,292,845; U.S. Pat. No. 4,798,081; U.S. Pat.No. 5,089,321 and by J. C. Randall, Rev. Macromol. Chem. Phys., C29, pp.201-317 (1989), the disclosures of all of which are incorporated hereinby reference.

In analytical temperature rising elution fractionation analysis (asdescribed in U.S. Pat. No.4,798,081 and abbreviated herein as “ATREF”),the polymer, polymer composition or article to be analyzed is dissolvedin a suitable hot solvent (for example, trichlorobenzene) and allowed tocrystallized in a column containing an inert support (stainless steelshot) by slowly reducing the temperature. The column is equipped withboth a refractive index detector and a differential viscometer (DV)detector. An ATREF-DV chromatogram curve is then generated by elutingthe crystallized polymer sample from the column by slowly increasing thetemperature of the eluting solvent (trichlorobenzene). The ATREF curveis also frequently called the short chain branching distribution (SCBD)or composition distribution (CD) curve, since it indicates how evenlythe comonomer (for example, 1-octene) is distributed throughout thesample in that as elution temperature decreases, comonomer contentincreases. The refractive index detector provides the short chaindistribution information and the differential viscometer detectorprovides an estimate of the viscosity average molecular weight. Thecomposition distribution and other compositional information can also bedetermined using crystallization analysis fractionation such as theCRYSTAF fractionalysis package available commercially from PolymerChar,Valencia, Spain.

Preferred homogeneously branched ethylene polymers (such as, but notlimited to, substantially linear ethylene polymers) have a singlemelting peak between −30 and 150° C., as determined using differentialscanning calorimetry (DSC), as opposed to traditional Zieglerpolymerized heterogeneously branched ethylene polymers (for example,LLDPE and ULDPE or VLDPE) which have two or more melting points.

The single melting peak is determined using a differential scanningcalorimeter standardized with indium and deionized water. The methodinvolves about 5-7 mg sample sizes, a “first heat” to about 180° C.which is held for 4 minutes, a cool down at 10° C./min. to −30° C. whichis held for 3 minutes, and heat up at 10° C./min. to 150° C. to providea “second heat” heat flow vs. temperature curve from which the meltingpeak(s) is obtained. Total heat of fusion of the polymer is calculatedfrom the area under the curve.

The at least one homogeneously branched ethylene interpolymer to beirradiated and/or crosslinked has a density at 23° C. less than 0.90g/cm³, preferably less than or equal to 0.88 g/cm³, more preferably lessthan or equal to 0.87 g/cm³, and especially in the range of 0.86 g/cm³to 0.875 g/cm³, as measured in accordance with ASTM D792.

Preferably, the homogeneously branched ethylene interpolymer ischaracterized as having a melt index less than 100 g/10 minutes, morepreferably less than 30, most preferably less than 10 g/10 minutes or inthe range of 3 to 12 g/10 minutes, as determined in accordance with ASTMD-1238, Condition 190° C./2.16 kilogram (kg). ASTM D-1238, Condition190° C./2.16 kilogram (kg) are referred to herein as “I₂ melt index”.

The homogeneously branched ethylene polymers for use in the inventioncan be either a substantially linear ethylene polymer or a homogeneouslybranched linear ethylene polymer.

The term “linear” as used herein means that the ethylene polymer doesnot have long chain branching. That is, the polymer chains comprisingthe bulk linear ethylene polymer have an absence of long chainbranching, as in the case of traditional linear low density polyethylenepolymers or linear high density polyethylene polymers made using Zieglerpolymerization processes (for example, U.S. Pat. No. 4,076,698 (Andersonet al.)), sometimes called heterogeneous polymers. The term “linear”does not refer to bulk high pressure branched polyethylene,ethylene/vinyl acetate copolymers, or ethylene/vinyl alcohol copolymerswhich are known to those skilled in the art to have numerous long chainbranches.

The term “homogeneously branched linear ethylene polymer” refers topolymers having a narrow short chain branching distribution and anabsence of long chain branching. Such “linear” uniformly branched orhomogeneous polymers include those made as described, for example, inU.S. Pat. No. 3,645,992 (Elston) and those made, for example, usingso-called single site catalysts in a batch reactor having relativelyhigh ethylene concentrations (as described in U.S. Pat. No. 5,026,798(Canich) or in U.S. Pat. No. 5,055,438 (Canich)) or those made usingvanadium catalysts or those made using constrained geometry catalysts ina batch reactor also having relatively high olefin concentrations (asdescribed in U.S. Pat. No. 5,064,802 (Stevens et al.) or in EP 0 416 815A2 (Stevens et al.)).

Typically, homogeneously branched linear ethylene polymers areethylene/α-olefin interpolymers, wherein the α-olefin is at least oneC₃-C₂₀ α-olefin (for example, propylene, 1-butene, 1-pentene,4-methyl-1-pentene, 1-heptene, 1-hexene, 1-octene and the like) andpreferably the at least one C₃-C₂₀ α-olefin is 1-butene, 1-hexene,1-heptene or 1-octene. Most preferably, the ethylene/α-olefininterpolymer is a copolymer of ethylene and a C₃-C₂₀ α-olefin, andespecially an ethylene/C₄-C₈ α-olefin copolymer such as anethylene/1-octene copolymer, ethylene/1-butene copolymer,ethylene/1-pentene copolymer or ethylene/1-hexene copolymer.

Suitable homogeneously branched linear ethylene polymers for use in theinvention are sold under the designation of TAFMER by Mitsui ChemicalCorporation and under the designations of EXACT and EXCEED resins byExxon Chemical Company.

The term “substantially linear ethylene polymer” as used herein meansthat the bulk ethylene polymer is substituted, on average, with about0.01 long chain branches/1000 total carbons to about 3 long chainbranches/1000 total carbons (wherein “total carbons” includes bothbackbone and branch carbons). Preferred polymers are substituted withabout 0.01 long chain branches/1000 total carbons to about 1 long chainbranches/1000 total carbons, more preferably from about 0.05 long chainbranches/1000 total carbons to about 1 long chain branched/1000 totalcarbons, and especially from about 0.3 long chain branches/1000 totalcarbons to about 1 long chain branches/1000 total carbons.

As used herein, the term “backbone” refers to a discrete molecule, andthe term “polymer” or “bulk polymer” refers, in the conventional sense,to the polymer as formed in a reactor. For the polymer to be a“substantially linear ethylene polymer”, the polymer must have at leastenough molecules with long chain branching such that the average longchain branching in the bulk polymer is at least an average of from about0.01/1000 total carbons to about 3 long chain branches/1000 totalcarbons.

The term “bulk polymer” as used herein means the polymer which resultsfrom the polymerization process as a mixture of polymer molecules and,for substantially linear ethylene polymers, includes molecules having anabsence of long chain branching as well as molecules having long chainbranching. Thus a “bulk polymer” includes all molecules formed duringpolymerization. It is understood that, for the substantially linearpolymers, not all molecules have long chain branching, but a sufficientamount do such that the average long chain branching content of the bulkpolymer positively affects the melt rheology (that is, the shearviscosity and melt fracture properties) as described herein below andelsewhere in the literature.

Long chain branching (LCB) is defined herein as a chain length of atleast one (1) carbon less than the number of carbons in the comonomer,whereas short chain branching (SCB) is defined herein as a chain lengthof the same number of carbons in the residue of the comonomer after itis incorporated into the polymer molecule backbone. For example, asubstantially linear ethylene/1-octene polymer has backbones with longchain branches of at least seven (7) carbons in length, but it also hasshort chain branches of only six (6) carbons in length.

Long chain branching can be distinguished from short chain branching byusing ¹³C nuclear magnetic resonance (NMR) spectroscopy and to a limitedextent, for example, for ethylene homopolymers, it can be quantifiedusing the method of Randall, (Rev. Macromol.Chem. Phys., C29 (2&3),p.285-297 (1989)), the disclosure of which is incorporated herein byreference. However as a practical matter, current ¹³C nuclear magneticresonance spectroscopy cannot determine the length of a long chainbranch in excess of about six (6) carbon atoms and as such, thisanalytical technique cannot distinguish between a seven (7) carbonbranch and a seventy (70) carbon branch. The long chain branch can be aslong as about the same length as the length of the polymer backbone.

Although conventional ¹³C nuclear magnetic resonance spectroscopy cannotdetermine the length of a long chain branch in excess of six carbonatoms, there are other known techniques useful for quantifying ordetermining the presence of long chain branches in ethylene polymers,including ethylene/1-octene interpolymers. For example, U.S. Pat. No.4,500,648, incorporated herein by reference, teaches that long chainbranching frequency (LCB) can be represented by the equation LCB=b/M_(w)wherein b is the weight average number of long chain branches permolecule and Mw is the weight average molecular weight. The molecularweight averages and the long chain branching characteristics aredetermined by gel permeation chromatography and intrinsic viscositymethods, respectively.

Two other useful methods for quantifying or determining the presence oflong chain branches in ethylene polymers, including ethylene/1-octeneinterpolymers are gel permeation chromatography coupled with a low anglelaser light scattering detector (GPC-LALLS) and gel permeationchromatography coupled with a differential viscometer detector (GPC-DV).The use of these techniques for long chain branch detection and theunderlying theories have been well documented in the literature. See,for example, Zimm, G. H. and Stockmayer, W. H., J. Chem. Phys., 17, 1301(1949) and Rudin, A., Modern Methods of Polymer Characterization, JohnWiley & Sons, New York (1991) pp. 103-112, the disclosures of both ofwhich are incorporated by reference.

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company,at the Oct. 4, 1994 conference of the Federation of Analytical Chemistryand Spectroscopy Society (FACSS) in St. Louis, Mo., presented datademonstrating that GPC-DV is indeed a useful technique for quantifyingthe presence of long chain branches in substantially linear ethylenepolymers. In particular, deGroot and Chum found that the level of longchain branches in substantially linear ethylene homopolymer samplesmeasured using the Zimm-Stockmayer equation correlated well with thelevel of long chain branches measured using ¹³C NMR.

Further, deGroot and Chum found that the presence of octene does notchange the hydrodynamic volume of the polyethylene samples in solutionand, as such, one can account for the molecular weight increaseattributable to octene short chain branches by knowing the mole percentoctene in the sample. By deconvoluting the contribution to molecularweight increase attributable to 1-octene short chain branches, deGrootand Chum showed that GPC-DV can be used to quantify the level of longchain branches in substantially linear ethylene/octene copolymers.

DeGroot and Chum also showed that a plot of Log(I₂, melt index) as afunction of Log(GPC Weight Average Molecular Weight) as determined byGPC-DV illustrates that the long chain branching aspects (but not theextent of long branching) of substantially linear ethylene polymers arecomparable to that of high pressure, highly branched low densitypolyethylene (LDPE) and are clearly distinct from ethylene polymersproduced using Ziegler-type catalysts such as titanium complexes andordinary homogeneous catalysts such as hafnium and vanadium complexes.

For substantially linear ethylene polymers, the empirical effect of thepresence of long chain branching is manifested as enhanced rheologicalproperties which are quantified and expressed in terms of gas extrusionrheometry (GER) results and/or melt flow, I₁₀/I₂, increases.

The substantially linear ethylene polymers used in the present inventionare a unique class of compounds that are further defined in U.S. Pat.No. 5,272,236, application Ser. No. 07/776,130, filed Oct. 15, 1991;U.S. Pat. No. 5,278,272, application Ser. No. 07/939,281, filed Sep. 2,1992; and U.S. Pat. No. 5,665,800, application Ser. No. 08/730,766,filed Oct. 16, 1996, each of which is incorporated herein by reference.

Substantially linear ethylene polymers differ significantly from theclass of polymers conventionally known as homogeneously branched linearethylene polymers described above and, for example, by Elston in U.S.Pat. No. 3,645,992. As an important distinction, substantially linearethylene polymers do not have a linear polymer backbone in theconventional sense of the term “linear” as is the case for homogeneouslybranched linear ethylene polymers.

Substantially linear ethylene polymers also differ significantly fromthe class of polymers known conventionally as heterogeneously branchedtraditional Ziegler polymerized linear ethylene interpolymers (forexample, ultra low density polyethylene, linear low density polyethyleneor high density polyethylene made, for example, using the techniquedisclosed by Anderson et al. in U.S. Pat. No. 4,076,698) in thatsubstantially linear ethylene interpolymers are homogeneously branchedpolymers. Further, substantially linear ethylene polymers also differfrom the class of heterogeneously branched ethylene polymers in thatsubstantially linear ethylene polymers are characterized as essentiallylacking a measurable high density or crystalline polymer fraction asdetermined using a temperature rising elution fractionation technique.

The substantially linear ethylene elastomers and plastomers for use inthe present invention is characterized as having

(a) melt flow ratio, I₁₀/I₂ ≧5.63,

(b) a molecular weight distribution, M_(w)/M_(n), as determined by gelpermeation chromatography and defined by the equation:

(M _(w) M _(n))≦(I₁₀/I₂)−4.63,

(c) a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂ and M_(w)/M_(n) within ten percent of the substantially linearethylene polymer and wherein the respective critical shear rates of thesubstantially linear ethylene polymer and the linear ethylene polymerare measured at the same melt temperature using a gas extrusionrheometer,

(d) a single differential scanning calorimetry, DSC, melting peakbetween −30° and 150° C., and

(e) a density less than or equal to 0.865 g/cm³.

Determination of the critical shear rate and critical shear stress inregards to melt fracture as well as other rheology properties such as“Theological processing index” (PI), is performed using a gas extrusionrheometer (GER). The gas extrusion rheometer is described by M. Shida,R. N. Shroff and L. V. Cancio in Polymer Engineering Science, Vol.17,No.11, p. 770 (1977) and in Rheometers for Molten Plastics by JohnDealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99, thedisclosures of both of which are incorporated herein by reference.

The processing index (PI) is measured at a temperature of 190° C., atnitrogen pressure of 2500 psig using a 0.0296 inch (752 microns)diameter (preferably a 0.0143(363 microns) inch diameter die for highflow polymers, for example, 50-100 I₂ melt index or greater), 20:1 L/Ddie having an entrance angle of 180°. The GER processing index iscalculated in millipoise units from the following equation:

PI=2.15×10⁶ dyne/cm²/(1000× shear rate),

where: 2.15×10⁶ dyne/cm²(215 MPa) is the shear stress at 2500 psi (176kg/cm²), and the shear rate is the shear rate at the wall as representedby the following equation:

32 Q′/(60 sec/min)(0.745)(Diameter×2.54 cm/in)³,

 where:

Q′ is the extrusion rate (gms/min),

0.745 is the melt density of polyethylene (gm/cm³), and

Diameter is the orifice diameter of the capillary (inches).

The PI is the apparent viscosity of a material measured at apparentshear stress of 2.15×10⁶ dyne/cm² (215 MPa).

For substantially linear ethylene polymers, the PI is less than or equalto 70 percent of that of a conventional linear ethylene polymer havingan I₂, M_(w)/M_(n) and density each within ten percent of thesubstantially linear ethylene polymer.

An apparent shear stress vs. apparent shear rate plot is used toidentify the melt fracture phenomena over a range of nitrogen pressuresfrom 5250 to 500 psig(369 to 35 kg/cm²) using the die or GER testapparatus previously described. According to Ramamurthy in Journal ofRheology, 30(2), 337-357, 1986, above a certain critical flow rate, theobserved extrudate irregularities may be broadly classified into twomain types: surface melt fracture and gross melt fracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular gloss to the more severe form of“sharkskin”. In this disclosure, the onset of surface melt fracture ischaracterized at the beginning of losing extrudate gloss at which thesurface roughness of extrudate can only be detected by 40×magnification. The critical shear rate at onset of surface melt fracturefor the substantially linear ethylene polymers is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a linear ethylene polymer having about the same I₂ andM_(w)/M_(n). Preferably, the critical shear stress at onset of surfacemelt fracture for the substantially linear ethylene polymers of theinvention is greater than 2.8×106 dyne/cm² (280 MPa).

Gross melt fracture occurs at unsteady flow conditions and ranges indetail from regular (alternating rough and smooth, helical, etc.) torandom distortions. For commercial acceptability (for example, in blownfilm products), surface defects should be minimal, if not absent. Thecritical shear rate at onset of surface melt fracture (OSMF) andcritical shear stress at onset of gross melt fracture (OGMF) will beused herein based on the changes of surface roughness and configurationsof the extrudates extruded by a GER. For the substantially linearethylene polymers used in the invention, the critical shear stress atonset of gross melt fracture is preferably greater than 4×10⁶ dyne/cm²(400 MPa).

For the processing index determination and for the GER melt fracturedetermination, substantially linear ethylene polymers are tested withoutinorganic fillers and do not have more than 20 ppm (parts per million)aluminum catalyst residue. Preferably, however, for the processing indexand melt fracture tests, substantially linear ethylene polymers docontain antioxidants such as phenols, hindered phenols, phosphites orphosphonites, preferably a combination of a phenol or hindered phenoland a phosphite or a phosphonite.

The molecular weights and molecular weight distributions are determinedby gel permeation chromatography (GPC). A suitable unit is a Waters 150Chigh temperature chromatographic unit equipped with a differentialrefractometer and three columns of mixed porosity where columns aresupplied by Polymer Laboratories and are commonly packed with pore sizesof 10³, 10⁴, 10⁵ and 10⁶ Å. For ethylene polymers, the unit operatingtemperature is about 140° C. and the solvent is 1,2,4-trichlorobenzene,from which about 0.3 percent by weight solutions of the samples areprepared for injection. Conversely, for the substantially hydrogenatedblock polymers, the unit operating temperature is about 25° C. andtetrahydrofuran is used as the solvent. A suitable flow rate is about1.0 milliliters/minute and the injection size is typically about 100microliters.

For the ethylene polymers where used in the present invention, themolecular weight determination with respect to the polymer backbone isdeduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience, Polymer Letters, Vol. 6, p. 621,1968, the disclosure of whichis incorporated herein by reference) to derive the following equation:

M_(polyethylene)=a*(M_(polystyrene))^(b.)

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: Mj=(Σw_(i)(M_(i) ^(J)))^(j). Where w_(i) is the weight fractionof the molecules with molecular weight M_(i) eluting from the GPC columnin fraction i and j=1 when calculating M_(w) and j=−1 when calculatingM_(n).

For the at least one homogeneously branched ethylene polymer used in thepresent invention, the M_(w)/M_(n) is preferably less than 3.5, morepreferably less than 3.0, most preferably less than 2.5, and especiallyin the range of from about 1.5 to about 2.5 and most especially in therange from about 1.8 to about 2.3.

Substantially linear ethylene polymers are known to have excellentprocessability, despite having a relatively narrow molecular weightdistribution (that is, the M_(w)/M_(n) ratio is typically less than3.5). Surprisingly, unlike homogeneously and heterogeneously branchedlinear ethylene polymers, the melt flow ratio (I₁₀/I2) of substantiallylinear ethylene polymers can be varied essentially independently of themolecular weight distribution, M_(w)/M_(n). Accordingly, especially whengood extrusion processability is desired, the preferred ethylene polymerfor use in the present invention is a homogeneously branchedsubstantially linear ethylene interpolymer.

Suitable constrained geometry catalysts for use manufacturingsubstantially linear ethylene polymers include constrained geometrycatalysts as disclosed in U.S. application Ser. No. 07/545,403, filedJul. 3, 1990; U.S. application Ser. No. 07/758,654, filed Sep. 12, 1991;U.S. Pat. No. 5,132,380 (application Ser. No. 07/758,654); U.S. Pat. No.5,064,802 (application Ser. No. 07/547,728); U.S. Pat. No. 5,470,993;U.S. Pat. No. 5,453,410 U.S. Pat. No. 5,374,696 application Ser. No.08/08,003); U.S. Pat. No. 5,532,394U.S. Pat. No. 5,494,874 and U.S. Pat.No. 5,189,192, the teachings of all of which are incorporated herein byreference.

Suitable catalyst complexes may also be prepared according to theteachings of WO 93/08199, and the patents issuing therefrom, all ofwhich are incorporated herein by reference. Further, themonocyclopentadienyl transition metal olefin polymerization catalyststaught in U.S. Pat. No. 5,026,798, which is incorporated herein byreference, are also believed to be suitable for use in preparing thepolymers of the present invention, so long as the polymerizationconditions substantially conform to those described in U.S. Pat. No.5,272,236; U.S. Pat. No. 5,278,272 and U.S. Pat. No. 5,665,800,especially with strict attention to the requirement of continuouspolymerization. Such polymerization methods are also described inPCT/US92/08812 (filed Oct. 15, 1992).

The foregoing catalysts may be further described as comprising a metalcoordination complex comprising a metal of groups 3-10 or the Lanthanideseries of the Periodic Table of the Elements and a delocalize β-bondedmoiety substituted with a constrain-inducing moiety, said complex havinga constrained geometry about the metal atom such that the angle at themetal between the centroid of the delocalized, substituted pi-bondedmoiety and the center of at least one remaining substituent is less thansuch angle in a similar complex containing a similar pi-bonded moietylacking in such constrain-inducing substituent, and provided furtherthat for such complexes comprising more than one delocalized,substituted pi-bonded moiety, only one thereof for each metal atom ofthe complex is a cyclic, delocalized, substituted pi-bonded moiety. Thecatalyst further comprises an activating cocatalyst.

Suitable cocatalysts for use herein include polymeric or oligomericaluminoxanes, especially methyl aluminoxane, as well as inert,compatible, noncoordinating, ion-forming compounds. So-called modifiedmethyl aluminoxane (MMAO) is also suitable for use as a cocatalyst. Onetechnique for preparing such modified aluminoxane is disclosed in U.S.Pat. No. 5,041,584, the disclosure of which is incorporated herein byreference. Aluminoxanes can also be made as disclosed in U.S. Pat. No.5,218,071; U.S. Pat. No. 5,086,024; U.S. Pat. No. 5,041,585; U.S. Pat.No. 5,041,583; U.S. Pat. No. 5,015,749; U.S. Pat. No. 4,960,878; andU.S. Pat. No. 4,544,762, the disclosures of all of which areincorporated herein by reference.

Aluminoxanes, including modified methyl aluminoxanes, when used in thepolymerization, are preferably used such that the catalyst residueremaining in the (finished) polymer is preferably in the range of fromabout 0 to about 20 ppm aluminum, especially from about 0 to about 10ppm aluminum, and more preferably from about 0 to about 5 ppm aluminum.In order to measure the bulk polymer properties (for example, PI or meltfracture), aqueous HCl is used to extract the aluminoxane from thepolymer. Preferred cocatalysts, however, are inert, noncoordinating,boron compounds such as those described in EP 520732, the disclosure ofwhich is incorporated herein by reference.

Substantially linear ethylene are produced via a continuous (as opposedto a batch) controlled polymerization process using at least one reactor(for example, as disclosed in WO 93/07187, WO 93/07188, and WO 93/07189,the disclosure of each of which is incorporated herein by reference),but can also be produced using multiple reactors (for example, using amultiple reactor configuration as described in U.S. Pat. No. 3,914,342,the disclosure of which is incorporated herein by reference) at apolymerization temperature and pressure sufficient to produce theinterpolymers having the desired properties. The multiple reactors canbe operated in series or in parallel, with at least one constrainedgeometry catalyst employed in at least one of the reactors.

Substantially linear ethylene polymers can be prepared via thecontinuous solution, slurry, or gas phase polymerization in the presenceof a constrained geometry catalyst, such as the method disclosed in EP416,815-A, the disclosure of which is incorporated herein by reference.The polymerization can generally be performed in any reactor systemknown in the art including, but not limited to, a tank reactor(s), asphere reactor(s), a recycling loop reactor(s) or combinations thereofand the like, any reactor or all reactors operated partially orcompletely adiabatically, nonadiabatically or a combination of both andthe like. Preferably, a continuous loop-reactor solution polymerizationprocess is used to manufacture the substantially linear ethylene polymerused in the present invention.

In general, the continuous polymerization required to manufacturesubstantially linear ethylene polymers may be accomplished at conditionswell known in the prior art for Ziegler-Natta or Kaminsky-Sinn typepolymerization reactions, that is, temperatures from 0 to 250° C. andpressures from atmospheric to 1000 atmospheres (100 MPa). Suspension,solution, slurry, gas phase or other process conditions may be employedif desired.

A support may be employed in the polymerization, but preferably thecatalysts are used in a homogeneous (that is, soluble) manner. It will,of course, be appreciated that the active catalyst system forms in situif the catalyst and the cocatalyst components thereof are added directlyto the polymerization process and a suitable solvent or diluent,including condensed monomer, is used in said polymerization process. Itis, however, preferred to form the active catalyst in a separate step ina suitable solvent prior to adding the same to the polymerizationmixture.

In preferred embodiments, for olefin polymers in general and forethylene polymers made in solution processes in particular, methods andprocedures are employed to ensure low or no gels are made duringpolymerization or are present in the resultant polymer product. Suchmethods and procedures include introducing a very small amount of animpurity into the feed stream to temporarily poison the active catalystimmediately at the point of feed injection into the reactor orpolymerization vessel. This method or procedure provides for a slightdelay of the initial reaction (polymerization), thereby permittingpolymerization to proceed after the feed is sufficiently mixed withregard to reactants and reactor contents. Suitable impurities include,but are not limited to, water, carbon dioxide, alcohols, acids andesters. In a generally preferred method, a small fraction of the recyclefeed stream that is set up to bypass purification equipment and/orpurifying conditions is reintroduced in the reactor or polymerizationvessel. These recycle impurities typically include finishing additivessuch as, for example, processing aids (for example, calcium stearate andfluoropolymers), catalyst deactivators, antioxidants and other thermalstabilizers as well as polymerization by-products or decompositionproducts such as water.

The homogeneously branched ethylene interpolymers (for example,substantially linear ethylene polymers and homogeneously branched linearethylene polymers) used in the present invention are interpolymers ofethylene with at least one C₃-C₂₀ α-olefin and/or C₄-C₁₈ diolefin.Copolymers of ethylene and an α-olefin of C₃-C₂₀ carbon atoms areespecially preferred. The term “interpolymer” as discussed above is usedherein to indicate a copolymer, or a terpolymer, where, at least oneother comonomer is polymerized with ethylene or propylene to make theinterpolymer.

Suitable unsaturated comonomers useful for polymerizing with ethyleneinclude, for example, ethylenically unsaturated monomers, conjugated ornon-conjugated dienes, polyenes, etc. Examples of such comonomersinclude C₃-C₂₀ α-olefins such as propylene, isobutylene, 1-butene,1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene,1-decene, and the like. Preferred comonomers include propylene,1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, and1-octene, and 1-octene is especially preferred. Other suitable monomersinclude styrene, halo- or alkyl-substituted styrenes,vinylbenzocyclobutane, 1,4-hexadiene, 1,7-octadiene, and naphthenics(for example, cyclopentene, cyclohexene and cyclooctene).

In one preferred embodiment, at least one substantially hydrogenatedblock polymer is blended with at least one substantially linear ethylenepolymer. In another preferred embodiment, at least one substantiallyhydrogenated block polymer is blended with at least one polypropylenepolymer. Suitable polypropylene polymers for use in the invention,including random block propylene ethylene polymers, are available from anumber of manufacturers, such as, for example, Montell Polyolefins andExxon Chemical Company. From Exxon, suitable polypropylene polymers aresupplied under the designations ESCORENE and ACHIEVE.

Other polymers that can be blended with either the substantiallyhydrogenated block polymer or the homogeneously branched ethyleneinterpolymer include, for example, but are not limited to, substantiallyhydrogenated block polymers, styrene block polymers, substantiallylinear ethylene polymers, homogeneously branched linear ethylenepolymers, heterogeneously branched linear ethylene (including linear lowdensity polyethylene (LLDPE), ultra or very low density polyethylene(ULDPE or VLDPE) medium density polyethylene (MDPE) and high densitypolyethylene (HDPE)), high pressure low density polyethylene (LDPE),ethylene/acrylic acid (EAA) copolymers, ethylene/methacrylic acid (EMAA)copolymers, ethylene/acrylic acid (EAA) ionomers, ethylene/methacrylicacid (EMAA) ionomers, ethylene/vinyl acetate (EVA) copolymers,ethylene/vinyl alcohol (EVOH) copolymers, polypropylene homopolymers andcopolymers, ethylene/propylene polymers, ethylene/styrene interpolymers,graft-modified polymers (for example, maleic anhydride graftedpolyethylene such as LLDPE g-MAH), ethylene acrylate copolymers (forexample, ethylene/ethyl acrylate (EEA) copolymers, ethylene/methylacrylate (EMA), and ethylene/methmethyl acrylate (EMMA) copolymers),polybutylene (PB), ethylene carbon monoxide interpolymer (for example,ethylene/carbon monoxide (ECO), copolymer, ethylene/acrylic acid/carbonmonoxide (EAACO) terpolymer, ethylene/methacrylic acid/carbon monoxide(EMMCO) terpolymer, ethylene/vinyl acetate/carbon monoxide (EVACO)terpolymer and styrene/carbon monoxide (SCO)), chlorinated polyethyleneand mixtures thereof.

EXPERIMENTAL

In an evaluation to determine the effects of irradiation under differentatmospheres with different stabilization packages, a substantiallylinear ethylene polymer, AFFINITY™ elastomer 8200 from The Dow ChemicalCompany, was selected. This polymer was an ethylene/1-octeneinterpolymer, made using a constrained geometry catalyst system and hada target density of 0.87 g/cm³ and an I₂ melt index of 5 g/10 min. Asmanufactured, the polymer also contained 500 ppm of Iragnox 1076, aphenolic antioxidant supplied by Ciba Specialty Chemicals, and 800 ppmof Sandostab P-EPQ, diphosphonite supplied by Clariant Corp.

Other stabilizing additives used in this evaluation included Cyanox1790, a phenolic stabilizer from Cytec Industries Inc.; Chimissorb 944,a hindered amine, and Irgafos 168 (I-168), a phosphite stabilizer, bothfrom Ciba Specialty Chemical; and Agerite D, an aromatic aminestabilizer from Uniroyal Chemical. These other stabilizing additiveswere incorporated into the AFFINITY™ elastomer 8200 using a twin-screwextruder and individual master-batch concentrates (3 weight percent)containing the respective additive.

In a second evaluation, the polymer used was a substantiallyhydrogenated block polymer having a M_(w) of about 63,000 and apolydispersity of about 1.0.

Samples were melt-spun into 70 denier (avg.) fibers at about a 4gm/min/hole output rate. For samples based on the AFFINITY™ polymer,fibers were prepared using a melt temperature of 230° C. and a die witha 28 mil (0.71 mm) diameter and {fraction (L/D)} of 3.5. For samplesbased on the substantially hydrogenated block polymer, elastic fiberswere prepared using a melt temperature of 260° C. and a die having a 28mil (0.71 mm) diameter and a {fraction (L/D)} of 3.5.

To irradiate sample fibers under an inert or reduced oxygen atmosphere,a nitrogen purge was carried out in a fume hood. Six fiber spools wereplaced in a five-gallon size ZIPLOC™ bag. The ZIPLOC was partly sealedleaving an opening for a rubber hose that was connected to the nitrogengas source. The ZIPLOC bag was then placed in a Shield Pack SP Class EStyle 1.3 Pouch which was an aluminum bag with polyethylene liner. Therubber hose was then placed at the opening of ZIPLOC bag and nitrogenwas permitted to flow into the ZIPLOC bag for 3 hours. The nitrogen flowrate was adjusted so that the bag was maintained at a slightly inflatedstate during 3 hours. After the 3 hours nitrogen purge, the rubber hosewas removed while simultaneously and in a continuous motion lightlypressing on ZIPLOC bag to closing the opening.

Next, the Shield Pack was heat sealed to leave only about a one inch(2.5 cm) opening. The rubber hose was placed through this opening andthe nitrogen flow was turn on and permitted to purge for 10 minutes.After the 10-minute purge, the hose was removed and the edge of theopening was folded over and heat sealed while simultaneously and in acontinuous motion lightly pressing on the Shield Pack to prevent theentry of air.

The nitrogen padded fiber spools were then electron-beam irradiatedusing multiple passes at 3.2 Mrad per pass. Control 1, Example 1, andExamples 5 to 11 were cooled to about 23° C. after each pass. Controls 2and 3, and Examples 2 to 4 were cooled to 5° C. before each pass. Thebags were turned upside down for each pass. The multiple passes andcooling after each pass were done to avoid fusion of fibers duringE-beam radiation. The temperature of the fiber during E-beam radiationshould be lower than 45° C., preferably lower than 40° C. It was foundthat the sample temperature increased about 15° C. for each pass of 3.2Mrad radiation. Instead of an aluminum bag, a paper box was used forelectron-beam irradiation under air.

The following test methods were used to test the heat resistance offibers during dyeing and heat setting processes. To simulate dyeingconditions, a Teflon sheet was placed on a metal sheet and twelve fibersper sample was placed on the Teflon sheet with six (6) fibers in eachdirection. The six cross direction fibers were laid on top of the sixforward direction fibers. The fibers were all about 2.5 inches (6.4 cm)long. Scotch tape was used to attach the ends of the fibers on theTeflon sheet. The samples were then heated at 130° C. for 30 min. Thesamples were then cooled to about 23° C. and a determination of whetherfibers stuck or not at the over-laid cross points was made for eachsample. In this test, fibers that did not stick at the cross points wereconsidered to have passed the (simulated) dyeing test. To reduce testingtime, samples can be heated at 200° C. for 3 min instead of the 130° C.for 30 min.

To simulate heat set conditions, another Teflon sheet was placed on ametal sheet. One end of a fiber having a 2 ½ inch (6.4 cm) length wastaped onto the Teflon sheet with a Scotch tape. The fiber was stretchedto five inches (12.7 cm) (100% stretch) by hand and held under 100%stretch by taping the other end of the fiber. Three fibers were used foreach sample with fibers placed at about 2 inches (5.1 cm) of separationfrom each other. The stretched fibers were than placed in an oven at200° C. and the time for the sample to break was recorded. Tosuccessfully pass the heat setting test, the time for the sample tobreak must be longer than 1 minute.

Table 1 shows, fiber samples that were irradiated under air (Controls 1and 2), even at high radiation doses as well as with the incorporationof the thermal stabilizers, did not exhibit sufficient heat resistanceto pass the dyeing or heat setting tests. The samples were stuck afterheating at 130° C. for 30 min. Control sample 3 which was irradiatedunder nitrogen but without the incorporation of an amine stabilizerpassed the dyeing test failed the heat setting test since the fiberbroken when heated at 200° C. under 100% stretch for less than 1 minute.The control sample with antioxidant and without irradiation (Control 1)was stuck together after heating at 130° C. Inventive Examples 1 to 11all passed both the dyeing and heat setting tests. The InventiveExamples were irradiated under nitrogen and all contained at least oneamine stabilizer such as a hindered amine or aromatic amine and in manyinstances also contained additional additives such a hinder phenol and2phosphorus-containing stabilizer. The result shows surprisingsynergistic effects of radiation under nitrogen and the use of an aminestabilizer in regard to passing dyeing and heat setting processing.Table 1 also shows that the present invention permits a reduction inradiation dose (that is, to ≦20 Mrad).

TABLE 1 Effect of Irradiation Conditions on Heat Resistance of FibersSticky at Fiber Break 130° C. Time at 200° C. Irradiated C944/C1790 Gelwt. % for under 100% Sample Conditions (ppm) (xylene) 30 min stretch(min) Control 1 32 Mrad in air 2000/0   60 yes N/D* Control 2 22.4 Mradin air 2000/1000 N/D yes N/D* Control 3 22.4 Mrad in N₂   0 N/D no 0.6Control 4 0 2000/1000 N/D yes N/D  Example 1 32 Mrad in N₂ 2000 N/D no 2Example 2 22.4 Mrad in N₂ 2000/1000 N/D no 15 Example 3 22.4 Mrad in N₂2000/2000 N/D no 33 Example 4 22.4 Mrad in N₂ 2000/1000 + N/D no 18 1000ppm of I-168 Example 5 25.6 Mrad in N₂ 3000/0   N/D no 4 Example 6 25.6Mrad in N₂ Agerite D N/D no 28 (only) at 2000 ppm Example 7 32 Mrad inN₂ 2000/1000 77 no 4 Example 8 25.6 Mrad in N₂ 2000/1000 73 no 5 Example9 22.4 Mrad in N₂ 2000/1000 70 no 4 Example 10 19.2 Mrad in N₂ 2000/100061 no 7 Example 11 16 Mrad in N₂ 2000/1000 61 no 35 N/D: not determined.N/D*: not determines since samples were either melted or stuck togetherat 130° C.

The effect of electron-beam irradiation dosage on heat resistance isalso shown in Table 1 in Inventive Examples 7-11. Inventive Examples7-11 were irradiated at the same temperature (22° C.) with the samestabilization package (2000 ppm of Chimasorb and 1000 ppm of Cyanox1790). Expectedly the results show that increased irradiation dosage,increased the degree of crosslinking (as measured by weight percent gelin the xylene extraction test). But surprisingly and unexpectedly,although Control 1 (which was representative of the invention describedin WO 99/63021) had the same degree of crosslinking as InventiveExamples 10 and 11, the inventive examples exhibited far superior heatresistance. That is, Inventive Examples 10 and 11 which were irradiatedunder nitrogen and stabilized with an amine/phenol stabilizer packagepassed the dyeing and heat setting tests while Control 1 completelyfailed the simulated dyeing test and thus could not be tested for itsheat setting performance. These results suggest that crosslinkingresulting from electron-beam irradiation in air versus crosslinking fromelectron-beam irradiation under nitrogen exists as different networkstructures and/or occur via different mechanisms.

TABLE 2 Effect of Irradiation Temperature on Fiber Tenacity and HeatResistance Fiber Break Time at 200° E-beam C. under irradiation TenacityElongation 100% stretch condition (kg) (%) (min) Example 9 N₂ at 23° C.0.97 ± 0.06 400 ± 13 4 Example 2 N₂ at 10° C. 1.18 ± 0.03 390 ± 15 15

Also, surprisingly, Table 1 demonstrates that the invention permitslower dosages of irradiation for an equivalent degree of crosslinking.This result is very surprising and unexpected because ordinarily theskilled worker would expected less crosslinking for those samples whereoxygen is excluded or reduced and there a higher level of stabilization.Yet Inventive Examples 10 and 11 exhibited the same degree ofcrosslinking as Control 1 even though Inventive Examples 10 and 11 wereirradiated while oxygen was excluded or reduced and had slightly higheradditive concentrations.

Table 2 indicates that the lower irradiation temperatures, the moreimproved will be tenacity and heat resistance.

To demonstrate adequate service temperatures (that is, heat resistance)for dyeing and finishing and to demonstrate that fiber could besuccessfully converted, another evaluation was conducted to produce dyedwoven and knit goods. In this evaluation, elastic fibers comprising asubstantially linear ethylene polymer, e-beam irradiated under nitrogenwith amine stabilization (Example 12) were knitted in separatecombinations with polyester, cotton, or nylon fibers using an industrystandard 18-cut circular knitting machine equipped with positive unwinddevices for the elastic yarns. During the knitting, the draft ratiobetween the elastic yarns and the non-elastic yarns ranged from 2× to4×. This draft ratio produced a standard elastic circular knit fabricwhich ranged in weight from 7-11 oz./sq. yd. (248-389 cm³/mm²) with afabric count of 35-46 wales per inch (13.8-18.1 wales/cm) and 50-81courses per inch (19.7-31.9 courses/cm), and percent elastic from 8-18%.The elastic fibers were then covered with polyester textured filamentusing an industry standard yarn covering device. The yarn was used asthe filling yarn on a Jaquard rapier loom with a cotton warp. Thisproduced a 5% elastic 2×1 twill bottom weight fabric with elasticity inthe weft direction.

In practice, fabrics are heat-set for two reasons: (1) to stabilize thenon-elastic yarns to prevent shrinking; and (2) to modify the elasticpower or stretch of the fabric. In heat setting, the fabric is heldunder tension and passed through a tenter frame, wherein heat is appliedacross a range of temperatures for different fibers. For example, 100%polyester fibers are typically heat set at 210° C. for 1 minute tostabilize the fabric. Because of the limited service temperature ofSpandex, a polyester/spandex blend fabric would have to be heat set atlower temperatures (for example, 182-196° C.). Consequentially,polyester/spandex blend fabric is typically not fully stabilized andoften shrinks. Conversely, in this evaluation, Inventive Example 12exhibited a high service temperature that permitted full heat setting ofthe polyester. The heat-setting studies were conducted at 210° C. for 1minute on polyester/Inventive Example 12 knitted fabrics (InventiveExample 13). This inventive blend fabric retained its elasticity and didnot shrink in further processing. After heat setting, Inventive Example12 fibers were removed from one sample of the blend fabric and analyzedby optical microscopy. Under 40× magnification, the heat set InventiveExample fibers showed no damage due to heat exposure and maintainedmechanical properties. Under the same conditions, ethylene polymerelastic fibers that were E-beam irradiated in air with aminestabilization appeared broken at 40× magnification.

In a dyeing evaluation, once heat set, polyester/inventive Example 12knitted fabrics were exposed to a range of dyeing conditions to evaluatedyeability performance. Three different industry standard dyeingconditions were used in this evaluation which consisted of high pressuredispersed dyeing of polyester, acid dyeing of nylon, and reactive dyeingof cotton. The most rigorous conditions was the dispersed dyeing ofpolyester wherein temperatures ranged from 60° C. to 130° C. andreagents included soda ash, caustic soda, surfactant, dispersed dye,antifoaming agents and acetic acid for pH balancing. After dyeing andfinishing, the Inventive Example 13 retained its elasticity andexhibited uniform coloration. The Inventive Example 12 fibers buried inthe fabric structure did not accept dye or stain which is unlike Spandexwhich stains during dyeing processing and consequentially must berepeatedly rinsed to remove the stain to prevent bleeding and crockingin consumer use and washing. The Inventive Example 12 fibers wereremoved from the fabric and analyzed by optical microscopy. Like theInventive fibers after heat setting, these showed no damage due to thedyes or exposure to the other chemical reagents and maintained theirmechanical properties. After being subjected to the same dyeingconditions, under 40× magnification, the ethylene polymer fibers thatwere E-beam under air with amine stabilization were indented and/orstuck to PET fibers.

In another evaluation, the effect of e-beam irradiation under nitrogenand amine stabilization was investigated for fibers comprising asubstantially hydrogenated block polymer. The block polymer wascharacterized as having a molecular weight (Mw) of 63,000; apolydispersity of about 1.0, containing 32% by weight styrene beforehydrogenation and 40% by weight 1,2 addition. In this evaluation,Control 6 and Inventive Examples 14-16 were all E-beam irradiated at 10°C. and all samples, Control 5, Control 6 and Examples 14-16, contained1700 ppm of Irganox-1010 (a hindered phenolic stabilizer) and 2000 ppmof Chimassorb 944 (a hindered amine stabilizer). Table 3 shows theresults of the simulated heat setting and dyeing tests.

TABLE 3 Effect of E-beam Irradiation Conditions on Heat Resistance ofSubstantially Hydrogenated Block Polymer (SHBP). Stick Test at RadiationGel, wt. % 130° C. for 30 Fiber Break Sample Mrad (xylene) min Time(min) Control 5 0 0 stuck 0.3 Control 6 25.6, air 35.9 stuck N/D Example14 22.4, N₂ 53.7 slightly stuck 10 Example 15 25.6, N₂ 67.7 none 12Example 16 28.8, N₂ 74.3 none 13 N/D: not determines because the sampleeither melted or was stuck together at 200° C.

The results in Table 3 show that the SHBP samples that were E-beamirradiated under nitrogen and were stabilized with an amine/phenoliccombination (Inventive Examples 14-16) exhibited improved heatresistance and passed the simulated dyeing and heat setting tests.

We claim:
 1. A method of making an elastic article having improved heat resistance comprising the steps of (a) providing at least one elastic polymer or elastic polymer composition which contains at least one amine or nitrogen-containing stabilizer therein, (b) fabricating, forming or shaping the polymer or polymer composition into an article, and (c) during or after the fabrication, forming or shaping, subjecting the article to ionizing radiation while the article is in or under an inert or oxygen-reduced atmosphere wherein the elastic polymer is or the elastic polymer composition comprises at least one hydrogenated block polymer; wherein the hydrogenated block polymer is a substantially hydrogenated block polymer characterized as having: i) a weight ratio of conjugated diene monomer unit to vinyl aromatic monomer unit before hydrogenation of greater than or equal to 60:40; ii) a weight average molecular weight (M_(w)) before hydrogenation of from 30,000 to 150,000, wherein each vinyl aromatic monomer unit (a) has a weight average molecular weight, Mw_(a), of from about 5,000 to about 45,000 and each conjugated diene monomer unit (b) bas a weight average molecular weight, Mw_(b), of from about 12,000 to about 110,000; and iii) a hydrogenation level such that each vinyl aromatic monomer unit block is hydrogenated to a level of greater than 90 percent and each conjugated diene monomer unit block is hydrogenated to a level of greater than 95 percent, as determined, using UV-VIS spectrophotometry and proton NMR analysis.
 2. A method of making an elastic article having improved heat resistance comprising the steps of: (a) providing at least one hydrogenated block polymer, (b) fabricating, forming or shaping the block polymer into an article, and (c) during or after the fabrication, forming or shaping, subjecting the article to ionizing radiation while the article is in or under an inert atmosphere wherein the hydrogenated block polymer is a substantially hydrogenated block polymer characterized as having: i) a weight ratio of conjugated diene monomer unit to vinyl aromatic monomer unit before hydrogenation of greater than or equal to 60:40; ii) a weight average molecular weight (M_(w)) before hydrogenation of from 30,000 to 150,000, wherein each vinyl aromatic monomer unit (a) has a weight average molecular weight, Mw_(a), of from about 5,000 to about 45,000 and each conjugated diene monomer unit (b) has a weight average molecular weight Mw_(b), of from about 12,000 to about 110,000; and iii) a hydrogenation level such that each vinyl aromatic monomer unit block is hydrogenated to a level of greater than 90 percent and each conjugated diene monomer unit block is hydrogenated to a level of greater than 95 percent, as determined using UV-VIS spectrophotometry and proton NMR analysis.
 3. The method of claim 2, wherein the at least one hydrogenated block polymer contains at least one phenol or phosphite stabilizer. 